Vania



March 19, 1929. E. 1.. WIEGAND ELECTRIC HEATING DEVICE 1 Filed Nov. 24, 1925 Origina Attorneys Patented Mar. 19, 1929.

UNITED STATES PATENT QFFICE.

EDWIN L. WIEGAND, OF DORMONT, FEEMISYLVAETIA, ASSIGNGR TO EDWIN L. WIE- GAND COMPANY, OF PITTSBURGH, PENNSYLVANIA, A SUEZOR-ATION OF PENNSYL- vAivIA.

Application filed November 24, 1925, Serial No. 71,071. Renewed January 21, 1929.

of the' element or puncturing the sheath, and

which shall lend itself to economy of heat.

In my prior applications Serial Nos. 660,294, 697,446 and 743,663 filed respectively August 31, 1923, March 7, 1924, and October 15, 1924, I have disclosed certain new and very valuable electric heating units consisting of wire resistance elements submerged in refractory insulating material which in turn is closely embedded in a fiat faced metal sheath. This sheath is made of a metal which will withstand the working temperature desired and is generally madeleak tight to prevent the ingress of water, grease, or other decomposable and electrically conduct-ing substances, and is generally made rather thin in one dimension although its shape varies greatly according to the use desired, being straight or curved, long or short, broad or narrow, annular, serpentine, disk-like, or polygonal at pleasure. It is important, however, that means be provided whereby these can be secured to a support or applied to the working surface by means which shall not injure the insulation or draw the sheath away therefrom. Obviously nothing ought to pass through the body of the unit since it would tend to create leakage and would require special arrangement of the resistance unit to prevent short circuiting; while provision shouldbe made for expansion and contraction in the plane ofthe device.

In the drawings accompanying and forming a part of this application I have shown certain physical forms in which my inventive idea can be embodied although it will be understood that these are intended to be merely illustrative of the general principles of my invention and the specific construction may vary considerably without departing therefrom. Fig. 1 is a sectional view of a unit and its support corresponding to the line 11 of Fig. 2 and drawn to heroic scale; Fig. 2 is a bottom plan view of the portion of one of my improved heating units adjacent one end; Figs. 3 and 4 are bottom plan views of two widely dissimilar shapes of units equipped with my invention; Fig. 5 illustrates a ring unit attached to a stove id by my invention, the section of the unitcorresponding to the line 55 in Fig. 4; Fig. 6 shows another form of unit and support; 7 shows a heating unit fastened by way of its heating face; and Fig. 8 is a sectional view of another modification.

My improved heating units consist essentially of thin walled metal members 1 and 2 seamed together longitudinally at- 3 and tightly embracing the insulating material 4 in which the resistance element 5 is submerged. These members are preferably made oblong in cross section and thin relatively to their width so that the heat evolved in the resistance element may reach the object to be heated with a minimum of impediment, and

'for the same reason I prefer to use the least practicable thickness of insulating material between the resistance element and the sheath.

In order to secure such a unit to a support I preferably secure to one face thereof a shanked member which is also provided with a shoulder so disposed as to engage the sup port in advance of any other part of the unit. In Figs. 1 and 2 I have shown the member 2 as embossed at 6 about an aperture 7, the aperture receiving the shank 8 and the embossed recess receiving the head 9 of the fastening member, this head being here made polygonal so as not to turn. (See Fig. 2.) In this way the head is located inside the sheath while the embossing serves the double function of affording room for the head without touching the unit 5 and of preventing the head from turning. The shank 8 is here shown as hollow and internally threaded for reception of a screw 10 although it can be externally threaded as shown in Fig. 5 if desired, and in Fig. 8 I have shown the shank as constituting part of a rivet.

In Fig. 1 I have shown the unit as fastened to a heat insulating slab 12 such as soapstone, the same having an aperture 13 for the shank 8, and a shallow counterbore 14 surrounding said aperture where it traverses the receiving face 15. Care should be taken that this recess,

when used, be sufliciently shallow that the face of the boss 6 may engage the bottom thereof before any other part of the unit touches the face 15 lest the sheath (which is generally made of sheet metal) be drawn away from the insulation. My invention is equally present in case the recess is omitted as shown .in Fig. 5.

I have chosen for illustration in l a straight strip unit as illustrated in Figs. 2 and 3 although the same can be made of any desired shape to anclincluding the complete circle shown in Fig. l, and the number of fastenings may be as great or as small as desired or as necessitated by the size and weight of the parts. In case of a ring unit, however, I preferably employ three fastenings, equally spaced as shown in F ig. 4.

- In Fig. 5 I have shown such a ring unit as carried by a metal plate 20. I have here shown the fastenings as externally threaded bolts 21 having their heads 22 welded or brazed to the outer face of the member 2 but provided with shoulders 23 to take the strain of the nuts 24. It will be understood that this welding or brazing can be employed only in 'cases wherein the working temperature is restrained to a suitable point, either by a suitable restriction upon the rate of heat generation or a suitably rapid rate of heat dissipation. The employment of a metal supporting plate 20 in contact therewith is an example, since the heat is conducted away fromthis part sufficiently rapidly to minimize the danger of separation. In any event it will be understood that themetal of the 1 members l', 2, and also of the fastening members must be chosen with respect to the temperatures employed.

In Fig. 6 I'have shown a support 30 made of ceramic material such as porcelain, having its face recessed for the reception of the entire unit and the bottom of the groove being ribbed or ridged to modify the rate of heat transfer; this device and indeed all the modifications heretofore discussed exhibiting the safety features of my application filed Aucontact. Ordinarily the unit is best supported from the bottom but it is equally possible to fasten its working face to the members to be heated, as in Fig. 7 where I have shown part of a corn popping machine comprising a circular plate 40 having a marginal tate its securing and the head is preferably large and flat'to distribute the pressure of clinching the same so as to minimize disin- .tegration of the refractory. This mode of a tachment is especially important in securing my sheathed units to metallic supports such .as shown at 52 in Fig. 8, which are generally rather thin in section IVhenever there is any substantial inequality between the eX' pansion of the heating unit and thesupport the holes 13 and recesses I l are made of greater width than the fastening members which occupy the same as shown in Figs. 1, 5, 6, and 8,-and the fastening device is provided with a flat washer 53 to enable ready sliding of the parts.

It will be understood that a great many other modifications in detail are possible to 1 be made within the scope of my inventive idea and are intended to be covered by my claims. 7

Having thus described I claim is: r

1. In electric heating devices, in combination, a support-ing member, a unit comprising a resistance element surrounded by electrical insulating material and a s ieet metal sheath embracing said material, said sheath having substantially flat opposed walls in close contact withsuch insulating material, and a fastening device secured to one of said walls and projecting outwardly therefrom away from the other wall.

2. In electric heating devices, in combination, a rigid supporting member, aunit comprising a resistance element surrounded by electrical insulating material and a metallic my invention what sheath embracing said material, said sheath and a fastening device secured to one of said walls and projecting outwardly therefrom away from the other wall, said device having an abutment portion adapted to come into tension resisting relation with the supporting member before any otlierpart of said unit contacts said member.

3. In electric heating devices, in combination, a unit comprising a resistance element surrounded by electrical insulating material and a metallic sheath embracing said inaterial, said sheath having substantially flat opposed walls in close contact with such 'insulating material and said resistance element being dlstributed substantially uniformly throughout the entire chamber defined by said sheath, and a straight-shanked fastening device secured to one of the walls of said sheath and projecting away from said resistance element.

at. In electric heating devices, in combination, a unit comprising a resistance element surrounded by electrical insulating material and-a metallic sheath embracing said materiahsaid sheath having substantially fiatopposed walls in close contact with such insulating material, and a fastening device having a tension resisting shank and an enlarged head, said head being fastened to one of theflat walls of said sheath and said shank proJecting away from said unit upon the side which 1s away from the opposite wall thereof. 5. In electric heating devices, the combination with rigid support for a heating unit, of a heating unit comprising a hollow metal sheath having apair of substantially flat opposed faces, one of which is located in proximity to said support and an electric resistance element and an electrical insulating substance inside said sheath, said sheath making close contact with said substance, and a fastening device secured to the face of said sheath which is nearest said support, said support being apertured for the r ception of said fastening device and said fastening device including means for applying tension thereto, and a shoulder engaging said support for resisting said tension, independently of the stiffness of said sheath.

6. In electric heating devices, the combination with a supporting member of rigid material having a plurality of spaced apertures, of a heating unit comprising a hollow metal sheath having a pair of substantially flat opposed facesand an electric resistance element and an insulating substance inside said sheath, said sheath making close contact with said substance, one face of said sheath located in proximity to the surface of said support, and a plurality of fastening members secured to said last named face and traversing said apertures, said members being of smaller diameter than said apertures.

7. In electric heating devices, in combination, a heating unit comprising a hollow metal sheath having a pair of substantially flat opposed faces, and an electric resistance element and an electrical insulating substance inside said sheath, said sheath being embossed to define a recess between it and such insulating substance and such boss having a hole therein, and a fastening device having a head in said boss and a shank projecting through said hole, said shank adapted to enter a hole in a supporting device.

8. In electric heating devices, the combination with a support, of a hollow metal sheath having a hole in one wall only, a fastening device having a shank traversing said hole and secured to said supportand also having a head inside said sheath, refractory electrically insulating material tightly compacted inside said sheath and against said head, and a resistor element submerged in said material and overlying said head, said shank projecting in a direction away from the other wall ofsaid sheath.

9. In electrical heating devices, the combination of an electrically insulated metal sheathed resistor unit, and a bifurcated rivet having its head operatively secured to the metal sheath, the shank of said rivet projecting outwardly of said unit away from said sheath.

10. In electric heating devices, the combination of a sheet metal sheathed resistor unit, and a fastening member having a head and a shank, said head being operatively secured to one wall of said sheath and said shank projecting outwardly of said unit away from that wall of the sheath to which it is secured and adapted to secure said sheath to a support adjacent to that wall to which said head is secured.

11. In electrical heating devices, the combination with a. support of an electrically insulated metal she thed resistor unit in juxtaposition therewith, a fastening member having a head and a shank, said head operatively secured to that wall of the metal sheath which is next to said support and said shank secured to said support so as to secure said resistor unit thereto.

12. In an electrical heating device, the combination of a resistor, a hollow metal sheath enveloping said resistor and spaced therefrom, refractory material of electrically insulating and heat conducting nature filling the space between said resistor and sheath, and a plurality of fastening devices secured to said sheath at spaced points and adapted to fasten the same to a support.

13. In an electrical heat-ing device, the combination with an electric heating unit comprising a resistor, a hollow metal sheath, and electrically insulating material interposed between said resistor and sheath, of a support, and a plurality of fastening devices attached to said units at spaced points and securing the same loosely to said support 5 whereby relative thermal expansion and contraction are permitted.

14. In an electrical heating device, the combination with an electric heating unit comprising a resistor, a hollow metal sheath, and electrically insulating material interposed between said resistor and sheath, of a plurality of metallic fastening devices each having a head and a shank, the heads being fastened to one wall of said sheath at spaced points and the shanks projecting away from said sheath without traversing the same.

15. In an electrical heating device, the combination with an electric heating unit comprising a resistor, a hollow metal sheath, and

twcen said resistor and sheath, 'ofa plurality of flexible nietal fastening devices each having a head and bifurcated shank, the heads being fastened to one wall of said sheath at spaced point-s and the shanks projecting away from said sheath without traversing the same.

16. In an electrical heating device, the combination with an electric heating unit com- .prising a resistor, a hollow metal sheath, and electrically insulating material interposed between said resistor and sheath, of a support adjacent to one face of said sheath and having a plurality of spaced holes therein, a

plurality of fastening devices, one for each hole, each of said fastening devices secured to the wall of said sheath adjacent to sald support and said support being spaced slightly from said sheath at all points except adjacent to said fastening devices.

17. In an electrical heating device, the com- .holes therein, and fastening devices, one for each hole, secured to the adjacentface of said sheath and engaging SHKlSUPPOl't 1n sliding relatlon, said support being spaced from the adjacent wall of said sheath except near said fastening devices.

In testimony whereof I hereunto affix my signature.

EDWIN L. 'WIEGAND. 

